Valves are routinely used to control the flow of fluids in the production and processing of many products and materials. Failure of valve seals can cause loss or contamination of product flows being controlled by the valves. It is therefore desirable to identify early failure of seals before seal leakage can reach troublesome levels or contaminate the product. The avoidance of contamination is particularly essential in the preparation of products such as foods, beverages and medicines destined for human or animal consumption, for example.
Furthermore, many products are manufactured or processed using batch production methods and the cleaning of equipment such as vessels and lines between batches to avoid cross-contamination between different products, or to avoid build-up of moulds, fungi, bacteria, and other pathogens is at least desirable, if not essential. In such situations it is desirable to be able to confirm the presence of the correct cleaning or rinsing flows through the processing plant.
U.S. Pat. No. 4,655,253 describes a shut-off valve comprising a valve housing having two chambers joined by an axial passage bounded by valve seats. A valve body has two parts which are independently movable axially in the housing. Each part carries a seal that respectively co-operates with one of the seats to close between a chamber and the associated passage. In one embodiment, a leakage detection space is provided between the seats. Fluid leaking past the seats into this space is discharged via a channel to provide a visible signal indicating the leakage and preventing intermixing of respective fluids in the two chambers.
U.S. Pat. No. 5,361,802 describes a valve block having metallic electrodes. If a valve of the block fails to seal, fluid leakage closes a circuit between electrodes to generate a signal which is processed by an analyser to trigger an alarm identifying the defective valve.
U.S. Pat. No. 5,594,162 describes a gas leak detector that is adapted for fitting about the control stem of a valve to monitor the leakage of a hydrocarbon gas from the valve.
U.S. Pat. No. 5,616,829 describes a valve with a leak detector which monitors vibrations caused by leakage through the seats or a gland/packing assembly of the valve. If leakage is detected when the valve is closed the valve is driven further in the closing direction, e.g. until the leakage, and thus the vibrations, disappear.